Compared with the traditional optical system using a plurality of spherical surface components, aspheric surfaces are capable of keeping corresponding performances while effectively simplifying the structure of the system, thus being widely used. By using the aspheric surfaces, the components of the optical system usually can be fewer in number and lighter in weight. For this reason, the aspheric surfaces are widely applied in the fields of ultraviolet lithography, high-quality imaging systems, astronomical telescopes, high-density photomemory and the like.
Various methods and corresponding instruments exist in the field of aspheric surface measurement at present. Such instruments include profilers and coordinate measurement machines based on a contact stylus method, interferometers based on subaperture stitching, shearing interferometers, white-light scanning interferometers, interferometers based on zero compensation and partial zero compensation, interferometers based on computer-generated holography, double-wavelength interferometers, and the like. Compared with the aspects of high accuracy, flexibility requirements and the like of the existing aspheric surface measurement, the methods have some problems in measurement capacity and accuracy.
The profilers and coordinate measurement machines based on the contact pin method are time-consuming in measurement and have a risk of damaging the measured surfaces because of adopting a point-by-point contact measurement method; the interferometers based on subaperture stitching need a high-accuracy multi-dimensional rotary translation platform, and perform stitching and obtain the morphology of the whole measured surface by virtue of the overlapped area data of adjacent sub-apertures; the shear interferometers can introduce accumulative measurement errors while performing surface shape reconstruction on a slope integral because of usually measuring the slope information of the measured surface; and the interferometers using computer-generated holography and a zero compensation lens may have errors introduced by compensation components. The existing methods aforementioned have shortages in the aspects of measurement time, measurement accuracy, additional zero lens, clamp, universality, cost and the like.
The patent (US20020160672) discloses a method for measuring the surface shape of an aspheric surface and a wavefront by using a mechanical scanning interferometer. According to the patent, light at other positions is filtered out and prevented from entering into a detector to generate interference in a spatial filtering mode and based on a method for measuring an interference optical path difference from the vertex of the aspheric surface to a tangent line. In order to obtain the surface shape of the whole aspheric surface, according to the patent, a special length measurement interferometer is especially used for measuring the displacement of the measured aspheric surface driven by the translation platform. According to the patent, a point detector is used for measuring an optical path difference, and due to the point-by-point measurement, it takes dozens of minutes to measure a complete surface. The complexity and cost of the system are also increased by using an additional length measurement interferometer, thus reducing the reliability of the measurement to a certain extent.